What important physics idea is this question targeting?
This question is designed to assess whether students understand Newton's First Law: that objects in motion stay in motion, and so a force must be acting on the ball to make it stop. (I)
This question is designed to see if students incorrectly describe the force from the foot as being present after the kick. (C)
This question targets the student's ability to diagram Newton's Laws in a real-world setting. (V)
Which answer best describes what student A's response indicates about their physics understanding?
The student understands the action-reaction relationship between the foot and the ball and carried that through all three stages. However, the force of the ball must be less than the force of friction if the ball is going to slow down. (I)
They correctly identify gravity and friction as acting on the ball throughout, and they distinguish between contact and non-contact forces. However, they do not yet grasp that after the foot loses contact, there is no forward force — just unbalanced friction gradually slowing the ball. (C)
The response suggests they are connecting force, contact, and motion, but still need help refining how those ideas relate to each other. (V)
Which of the following options would best support Student B in being able to correctly respond to this question?
I’d use a digital simulation (like PhET’s Forces and Motion) so students can toggle forces on and off and see the results. I’d challenge them to get the object to move at constant speed and then slow down, and then have the class create free-body diagrams for each challenge scenario. (C)
I’d have them watch a slow-motion video of a soccer kick and describe what they see. Then I’d let them update their drawing based on the video and compare with other students.(I)
I would make students do a think-pair-share and then draw their results on the board up at the front of the room so we could make sure everyone agrees. (V)
Which answer best describes what student B's response indicates about their physics understanding?
They understand that friction acts throughout, so they clearly get what slows the ball down, and realize the foot's force disappears over time. After the first step, they mislabeled the foot force on the ball as a force instead of as inertia and Kate's foot as pressure instead of just force and gravity as pushing instead of pulling. I think they mostly understand forces but need help with getting terminology right. (I)
They correctly include gravity and friction and identify friction as opposing motion, suggesting a good understanding of friction forces. However, their idea that the foot’s force “shrinks” over time reveals is a common but wrong idea. They need help differentiating forces from other features of motion, like velocity or kinetic energy. (C)
This student is beginning to reason about how forces change across different stages of an interaction. They are clearly thinking carefully about how the ball’s behavior changes over time and how things like whether the foot is nearby affects what’s happening. They are using consistent language and representations to express their ideas. With continued exposure to more motion scenarios, they’ll refine their thinking and develop a stronger grasp of how forces operate. (V)
Which of the following options would best support Student B in being able to correctly respond to this question?
I’d ask the student to create a force diagram where they can only include forces from things that are touching the ball in the moment or acting from a distance (like gravity). This encourages them to check their reasoning about which forces are real and ongoing. We would then compare their diagrams to Newton's First Law.(C)
“I’d ask the student to estimate how much weaker the foot’s force is in each drawing — then we’d calculate how that relates to the ball's acceleration over time and when it would come to a stop. ” (I)
I’d have students create a storyboard showing how the forces on the ball change over time from before the kick to when it stops. This would help them visualize the phases of motion and build a more complete picture of the system. They could label their diagrams and narrate what’s happening to the forces. (V)